Battery Basics

Introduction

 As battery powered device increasing in ubiquity, system EE need to have solid understand of battery chemistry, capacity, aging, and charging and discharged curve. 

Overview

• Chemistry

  • Lithium ion/LIPO/Lithium Polymer - Rechargeable

    • Operating voltage: ~ 3V to 4.2V

  • Alkaline

    • Operating voltage: 0.9V to 1.5V

  • Nickel–cadmium battery (NiCD)

    • 1.2V nominal

  • Nickel-Metal Hydride  (NiMH) 

    • 1.2V nominal

• Capacity (measured in mAh)

  • Lithium ion

    • ~ 3000 mAh for a typical phone

  • Alkaline

    • ~1000 mAh for AAA battery

  • Nickel–cadmium battery (NiCD)

    • 1000 mAh

  • Nickel-Metal Hydride  (NiMH) 

    • 2500 - 2700 mAh

• Energy Density

  • Volume Metric Density (measured in W-HR/L)

    • Lithium Ion: 210

    • Nickel–cadmium battery (NiCD): 140

    • Nickel-Metal Hydride  (NiMH) : 180

• Charging Rate

  • Measured in C

    • 1 C means it takes an hour to finish chaging from 0% to 100%; 2C means it takes 30 mins to finish charging.

• Charging Curve

  • Lithum ion

    • Precharge/Trickle charging (Vbat < 2.1V) -> Constant Current -> Constant Voltage (taper off at vbat ~ 4.35V) -> Charging termination (0.02C)

      • termination is based on charging current falling  below a threshold rate, typically 0.02C to 0.07C

  • Nickel-Metal Hydride  (NiMH) 

    • Trickle charging -> Constant Current -> top-off charge -> Charging termination

Q&A

Why is Lithium Ion battery chosen for premium portable electronics such as a smart phone?

• • Lithium Ion battery has the highest energy density.

References and Further Reading:

" Recharging Alkaline Batteries : Fact or Fiction?", https://zbattery.com/Recharging-Alkaline-Batteries-Fact-or-Fiction 

"Battery Energy Density": https://forum.digikey.com/t/battery-energy-density/445?utm_adgroup=Battery%20Products&utm_source=google&utm_medium=cpc&utm_campaign=Dynamic%20Search_RLSA_Buyers&utm_term=&utm_content=Battery%20Products&gclid=CjwKCAjwjqT5BRAPEiwAJlBuBdy6wksR42v3cfwgH-gFmsifrNk9z1xg_K82YEDWmiR_GsrXdBnqmhoCfDoQAvD_BwE 

"Battery Charging", https://www.ti.com/lit/an/snva557/snva557.pdf?ts=1596610924925&ref_url=https%253A%252F%252Fwww.google.com%252F 

"Charging Lithium-ion", https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries#:~:text=Figure%203:Volts/capacity%20vs.%20time%20when%20charging%20lithium-ion.%20The%20capacity%20trails 

"Developing Affordable Mixed Signal power ysstems for Battery Charger Applications", http://www.rusmagnet.ru/2019/MANUALS/en027883.pdf